That reason I would never spend that sort of money on traffic detection is because much or most traffic in Class G is non transponding, so it's a near-complete waste of money.
Nobody should moan about somebody spending the money though; it's a free world. Lots of GA planes are worth £200k+ - so what?
What people do moan about is having a mandatory transponder, and that should not be the big deal that it is made out to be.